Some of the larger reports require a lot of memory to generate. You should have at least 128 MB RAM on the Windows computer that you're using to generate the report.
Report catalog is corrupted
Delete and recreate the Report Catalog object. Then try generating the report again. To create a Report Catalog object, you must have a NetWare volume in your eDirectory tree to install the report catalog files on.
You might not have completed the required reporting setup